Let's do this backwards:
4-D: The "4th Dimension" - the scratch and sniff cards. Complete and utter FAILURE. Nobody in my theater could smell anything at all except the cardboard it was printed on. We might as well have been sniffing our ticket stubs. Even my daughter, who was quite excited abot the gimmick, gave up by the third "scent", handed me the card, and said "I don't need this - it doesn't work." It was a silly idea to begin with, but something kids might have gotten a kick out of... if it worked... at ALL... which it didn't.
3-D: How about the 3-D? Mostly pointless, but then again most 3-D movies are. My biggest complaint it this: Why bother making a movie 3-D, but only do parts of it? Every live-action 3D movie I've seen including this one have many scenes and shots that aren't even in 3D. You can tell when you can take off your glasses and it's a strictly 2D image. I don't mean just certain whole scenes, but even just shots within a scene. For example within one dialogue scene the 3-D was used on only about every third cut, even if it was more of the same exact shot(?) So not only are they too lazy to shoot it in 3D, but they don't even convert the whole thing.
2D: The movie itself. Harmless, simple fun for the kids, although the actual new Spy Kids don't get to do much until the last third of the movie. The biggest problem: *SPOILER ALERT* was that even from the first trailers it was obvious Jeremy Piven was the villain, much less from every single scene in the movie. Yet they make a big deal of his predictable reveal. Was anyone surprised? *END SPOILER*
All in all what could have been a decent action flick for kids (and a restart to the franchise with new kids) is mostly a dud, due in large part to the heavily promoted "aromascope" gimmick which not only wasn't good.... it didn't even work.